1. Field of the Invention
The invention relates to an inductance element and a method for manufacturing the inductance element, and more particularly, relates to an inductance element which has a closed magnetic path structure, and a method for manufacturing the inductance element having a closed magnetic path structure.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2007-67081 (hereinafter, “Patent Document 1”) discloses an inductance element including a magnetic core with a flange, which is formed of ferrite, a coil wound around the magnetic core, and a soft magnetic resin layer with magnetic powder therein, which is formed to cover the coil.
However, the inductance element described in Patent Document 1 forms a closed magnetic path, and thus, when a direct current is superimposed, there will cause magnetic saturation in which the magnetic flux density B shows almost no increase even when the magnetic field H, that is, the current through the coil is increased. As a result, the inductance element has a problem that the slope of the BH curve, that is, the magnetic permeability μ becomes smaller, thereby significantly reducing the inductance value.
Japanese Patent Application Laid-Open No. 6-251946 (hereinafter, “Patent Document 2”) discloses an inductance part formed of a soft magnetic drum with a columnar section and enlarged flange sections on each end, a coil winding section wound around the columnar section, and a soft magnetic sleeve surrounding the soft magnetic drum and fitting the enlarged flange sections. The temperature coefficient of the soft magnetic drum and the temperature coefficient of the soft magnetic sleeve have opposite signs with respect to each other.
In the Patent Document 2 described above, permitting the respective temperature coefficients of the soft magnetic drum and soft magnetic sleeve to have opposite signs with respect to each other aims to cancel the two temperature coefficients each other to bring the temperature coefficient of the entire inductance part closer to substantially “0”. However, Patent Document 2 completely fails to include any disclosure of direct current superimposition characteristics, and thus completely fails to disclose the combination of temperature coefficients required and the range of the temperature characteristics required to improve the current superimposition characteristics, as a matter of course.